U.S. patent number 6,202,533 [Application Number 09/360,272] was granted by the patent office on 2001-03-20 for subcaliber device/blank firing adaptor for blowback operated or recoil operated weapons.
This patent grant is currently assigned to Armalite, Inc.. Invention is credited to John M. Miller, George L. Reynolds, S. Paul Reynolds.
United States Patent |
6,202,533 |
Reynolds , et al. |
March 20, 2001 |
Subcaliber device/blank firing adaptor for blowback operated or
recoil operated weapons
Abstract
The bolt of a blowback operated weapon is driven rearward by
multiplying the area acted upon by pressurized gas generated by a
subcaliber bulleted cartridge or a blank cartridge fired in a
subcaliber barrel inserted into the weapon barrel and attached to
the weapon barrel muzzle.
Inventors: |
Reynolds; George L. (Altona,
IL), Reynolds; S. Paul (Altona, IL), Miller; John M.
(Marietta, OH) |
Assignee: |
Armalite, Inc. (Geneseo,
IL)
|
Family
ID: |
25449643 |
Appl.
No.: |
09/360,272 |
Filed: |
July 26, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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924054 |
Aug 28, 1997 |
5983772 |
|
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Current U.S.
Class: |
89/29;
89/14.5 |
Current CPC
Class: |
F41A
21/10 (20130101); F41A 21/26 (20130101); F41A
33/00 (20130101); F42B 8/10 (20130101) |
Current International
Class: |
F42B
8/10 (20060101); F41A 21/00 (20060101); F41A
33/00 (20060101); F41A 21/10 (20060101); F41A
21/26 (20060101); F42B 8/00 (20060101); F42B
008/12 () |
Field of
Search: |
;89/14.5,29,30
;42/77 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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730030 |
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Jan 1943 |
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DE |
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1195205 |
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Jun 1965 |
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DE |
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340829 |
|
Nov 1989 |
|
EP |
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662545 |
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Aug 1929 |
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FR |
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1496220 |
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Sep 1967 |
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FR |
|
8102 |
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1894 |
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GB |
|
874 |
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1907 |
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GB |
|
Primary Examiner: Johnson; Stephen M.
Attorney, Agent or Firm: Woodard, Emhardt, Naughton Moriarty
& McNett
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of co-pending U.S.
patent application Ser. No. 08/924,054, filed Aug. 28, 1997, now
issued as U.S. Pat. No. 5,983,772.
Claims
What is claimed is:
1. A subcaliber cartridge and a firearm apparatus for firing a
projectile of the subcaliber cartridge, comprising:
a subcaliber barrel disposed within a barrel of the firearm, said
subcaliber barrel including a first primary booster area at one end
and a bore extending to an opposite muzzle end; and
a cartridge case adaptor including a second primary booster area,
said cartridge case adaptor positionable with respect to said
subcaliber barrel by a bolt of the firearm to form a volume between
said first primary booster area and said second primary booster
area, said cartridge case adaptor including a subcaliber cartridge
chamber coaxial with said subcaliber barrel bore, said chamber
having an enlarged neck portion,
wherein said volume communicates with said enlarged neck portion
when said subcaliber cartridge is disposed within said chamber
thereby allowing passage of pressurized gas from said chamber to
said volume when said subcaliber cartridge is fired and the
projectile of said subcaliber cartridge is positioned within said
enlarged neck portion.
2. The apparatus of claim 1, further including a centering ring
disposed between the firearm barrel and said subcaliber barrel.
3. The apparatus of claim 1, wherein said cartridge case adaptor is
reusable.
4. The apparatus of claim 1, wherein the projectile of said
subcaliber cartridge extends from said enlarged neck into said bore
of said subcaliber barrel when said subcaliber cartridge is
positioned in said chamber.
5. A method for increasing the blowback force created upon firing a
projectile of a subcaliber cartridge from a firearm,
comprising:
(a) providing a subcaliber barrel disposed within a barrel of the
firearm, said subcaliber barrel including a first primary booster
area at one end and a bore extending to an opposite muzzle end;
(b) providing a cartridge case adaptor including a second primary
booster area and a subcaliber cartridge chamber coaxial with said
subcaliber barrel bore, said subcaliber cartridge chamber including
an enlarged neck portion;
(c) inserting the subcaliber cartridge in the subcaliber cartridge
chamber;
(d) positioning said cartridge case adaptor with respect to said
subcaliber barrel with a bolt of the firearm to form a volume
between said second primary booster area and said first primary
booster area; and
(e) firing the firearm so pressurized gas passes through the
enlarged neck around the projectile to said volume.
6. A subcaliber cartridge and a firearm apparatus for firing the
subcaliber cartridge, comprising:
a subcaliber barrel positioned within a barrel of the firearm, said
subcaliber barrel including a first primary booster area at one end
and a bore extending to an opposite muzzle end; and
a cartridge case adaptor including a second primary booster area,
said cartridge case adaptor positionable with respect to said
subcaliber barrel by a bolt of the firearm to form a volume between
said first primary booster area and said second primary booster
area, said cartridge case adaptor including a subcaliber cartridge
chamber coaxial with said subcaliber barrel bore,
wherein said volume communicates with said chamber thereby allowing
passage of pressurized gas from said chamber to said volume when
the subcaliber cartridge is fired.
7. The apparatus of claim 6, further including a centering ring
disposed between the firearm barrel and said subcaliber barrel.
8. The apparatus of claim 6, wherein said cartridge case adaptor is
reusable.
9. The apparatus of claim 6, wherein said subcaliber cartridge
chamber includes an enlarged neck portion.
10. The apparatus of claim 9, wherein said volume communicates with
said enlarged neck when said subcaliber cartridge is disposed
within said chamber thereby allowing passage of pressurized gas
from said chamber to said volume when the subcaliber cartridge is
fired and a projectile of said cartridge is positioned within said
enlarged neck portion.
11. The apparatus of claim 9, wherein a projectile of said
subcaliber cartridge extends from said enlarged neck into said bore
of said subcaliber barrel when said subcaliber cartridge is
positioned in said chamber.
Description
BACKGROUND OF INVENTION
This invention is related to BLANK FIRING ADAPTOR, U.S. Pat. No.
5,438,907 by George Reynolds and John Miller, but is equipped with
a subcaliber barrel instead of a spigot, employs gas pressure
multiplier system and fires bulleted cartridges or blanks.
Medium caliber automatic weapons such as the Mk19, 40 mm machinegun
used by U.S. military forces require relatively expensive training
ammunition because of the relatively large size of the ammunition
used plus the fact that the Mk 19 is a machinegun. It is estimated
there are 300,000 Mk 19's in active use in the U.S. military
services. It is conservatively estimated that each gun is fired
100,000 rounds in training during the life of the weapon.
Conventional training rounds cost approximately $15 each, resulting
in a life cycle training cost for ammunition of $450 billion. Thus,
the cost of adequate training is very high for this very effective
weapon. Subcaliber devices which provide realistic training are
well known for use in most small arms weapons, but until the
present, none have been suitable for use with the Mk19 and similar
weapons.
SUMMARY OF PRESENT INVENTION
The present invention provides for realistic training by firing
relatively inexpensive subcaliber cartridges or blanks in
reloadable adaptors. With the cost of the subcaliber device/blank
firing adaptor at, say $500 each, the cost of the adaptor cases at
$5 each and the cost of the subcaliber cartridge or blank cartridge
at 25 cents each, the life cycle cost for firing 100,000 subcaliber
rounds through 300,000 Mk19's is approximately $9.1 billion, as
compared with $450 billion dollars with full caliber training
rounds. Use of the subcaliber device will result in a 98% cost
reduction for training ammunition compared to using the least
expensive full caliber training rounds.
The subcaliber device/blank firing adaptor powers a blowback or
recoil operated weapon so the weapon will function in normal
automatic fire. All loading, firing, safety, and stoppage
procedures normally performed by the gun crew are employed when
using the sibcaliber device/blank firing adaptor.
Firing with the subcaliber device/blank firing adaptor approximates
the feel and noise of firing full caliber service ammunition. The
trajectory of the subcaliber projectile nearly duplicates that of
fill caliber service ammunition. This closely matching trajectory
is especially valuable when using subcaliber tracer projectiles so
the soldier can become very familiar with the characteristics of
time of flight and trajectory arc of service rounds while firing
inexpensive subcaliber rounds.
The cartridge case adaptor which contains the subcaliber cartridge
or blank cartridge is easily and rapidly reloadable by soldiers
training in the field. Reloading is accomplished using a simple,
hand operated fixture which is not part of this patent.
Installation of the subcaliber device/blank firing adaptor requires
no special tools and is performed by the gun crew in the field,
requiring less than five minutes in the case of the Mk19
machinegun. All subcaliber device/blank adaptor components are low
technology, require no exotic materials, and are inexpensive to
manufacture. The blank firing adaptor uses standard, commonly
issued conventional rifle/machinegun blanks.
In the three subcaliber device embodiments of the invention three
different methods are used to multiply the force of the propellant
gas above the straight blowback force of the projected area of the
base of the projectile. In the blank firing adaptor embodiment, gas
is trapped by a vented muzzle disc at the front of the subcaliber
barrel to retain pressurized gas to apply sufficient force to
operate the weapon.
In the first embodiment, instead of reaction of the propellant gas
being only against the projectile, part of the reaction is
transmitted from a primary booster area to the weapon frame though
a subcaliber barrel inserted through the main gun barrel and
anchored to the muzzle of the main gun barrel.
In the second embodiment, in addition to the reaction of the
propellant gas against the primary booster area, as in the first
embodiment, a secondary chamber with a secondary booster area is
provided to trap gas to apply force for a longer period of time.
Propellant gas is released from the subcaliber cartridge chamber
into the secondary booster chamber when pressure in the subcaliber
chamber exceeds the strength of the subcaliber cartridge case wall
at the chamber vent, perforating the subcaliber cartridge case wall
at the subcaliber chamber vent. In this embodiment, gas escaping
into the secondary chamber of the adaptor pressurizes a larger area
(e.g. ten to twenty times greater) than the projected bore area of
the subcaliber cartridge projectile. Gas is trapped in the
secondary booster by the restriction of the gas vent which admitted
the highly pressurized gas from the subcaliber chamber, much as gas
is trapped in the gas cylinder of a conventional gas operated gun
mechanism.
The third embodiment is like the second embodiment except the
secondary chamber is vented to the atmosphere to limit the
operating force to that of the primary booster area by eliminating
force (rather than adding force) from the secondary booster. This
embodiment is required when a standard cartridge such as the 7.62
mm NATO is used, but which provides excess power with the Mk 19. It
is desirable to use standard 7.62 mm machinegun ammunition due to
its low cost and ready availability.
A fourth embodiment permits the subcaliber device to be converted
into a blank firing adaptor related to U.S. Pat. No. 5,438,907 by
the installation of a vented restrictor disc at the front of the
muzzle of the subcaliber barrel. The vented restrictor disc
sufficiently contains the blank generated pressurized gas to
operate the weapon. Blank cartridges operate at such low pressure
when operated with a large free volume, that the cartridge case
wall will not perforate at the booster vent to release gas into the
secondary booster chamber. The vented restrictor disc is retained
by a vented muzzle cap which also serves as a bullet trap in case a
bulleted cartridge is accidently fired when normally using blanks.
If a rifle grenade launching cartridge, which is much more powerful
than a blank, is accidently fired, the higher pressure of the
grenade cartridge bursts the vented restrictor disc, preventing the
high power of the grenade cartridge from damaging the gun
mechanism. The vented restrictor disc is inexpensive and easily
replaced.
In the first three embodiments the operating force of the
subcaliber cartridge is multiplied above that available through
straight blow-back by a factor equal to the ratio of the projected
area of the bore of the subcaliber cartridge to the area of the
total booster areas affected by the gas. This fully powers the
weapon while using a cartridge less than 1/20 the weight and 1/50
the cost of the least expensive training cartridge the weapon was
designed for. By adjusting the booster area(s), initial volume,
length of power stroke, diameter of perforation, projectile weight
and by selecting powder burning rate the subcaliber device and
cartridge can be designed to launch a subcaliber projectile at the
same velocity (or higher or lower) as the service projectile. Thus
the trajectory of the service round can be closely duplicated
provide realistic training. Tracer ammunition can be used where
range conditions permit, or ball ammunition can be used where dry
range conditions prohibit the use of tracers.
The total blowback force is equivalent to that generated by a full
caliber service round, but the reaction is primarily against the
gun itself through the subcaliber barrel and muzzle cap attached to
the muzzle of the weapon barrel instead of reacting only against
the projectile as in straight blow-back operation. In the case of
the 40 mm Mk19 subcaliber device using a 1.300 inch diameter
secondary booster area and firing a 0.308 diameter subcaliber
bullet, the effective total blowback area is approximately 19 times
the area of the subcaliber projectile. Thus it is possible to
obtain from approximately twenty grains of powder (when firing a
214 grain subcaliber projectile at approximately 790 feet per
second muzzle velocity) more than enough power to operate the Mk19
with its approximately 17 pound bolt.
The Mk19 is normally provided with a bag for catching empty
cartridge cases. After firing with the subcaliber device/blank
firing adaptor, the soldier in the field collects the empty
cartridge case adaptors from the catch bag and ejects the expended
subcaliber cartridge cases from the cartridge case adaptors. Fresh
subcaliber cartridges or blanks are inserted into the cartridge
case adaptors. and the cartridge links are repositioned on the
cartridge case adaptors. The cartridge case adaptors are re-linked
into a belt. This process is accomplished using a simple hand
operated fixture which is not part of this invention.
The basic principle of operation of the subcaliber device is
typical of other subcaliber devices, except a close ballistic match
is achieved between the subcaliber projectile and the service
projectile while powering the weapon. In straight blow-back
operated weapons,
MV of the bolt=MV of the projectile (neglecting shot start,
projectile engraving and friction)
where M=mass and V=velocity.
In the Mk 19 the projectile weighs approximately 0.6 lbs, and has a
muzzle velocity of 790 feet per second. The Mk 19 bolt weighs
approximately 17.25 lbs. Applying MV=MV;
(0.6 lb)(790 fps)=(17.25 lbs)(X fps), or X=approximately 27.5 feet
per second bolt velocity.
But in a subcaliber device, if the booster diameter is 1.30 inch
and the subcaliber projectile diameter is 0.308 inch, then the
ratio of the areas of the booster and the subcaliber projectile is
about 17.8/1. This means the subcaliber projectile at 0.308
caliber, if it has the same sectional density as the service
projectile, needs only weigh 1/17.8th of the service projectile to
provide the same effective reaction is the service projectile,
because:
F=PA where F=force, P=pressure, and A=area
With the same pressure acting on the projectile with its small area
and the booster with its large area. the force applied to the
larger area of the booster is in direct proportion to the ratio of
the large area to the small area.
Another way of stating this is that any diameter of subcaliber
projectile may be used, as long as its effective sectional density
is the same as that of the service projectile (if the subcaliber
projectile is to have the same muzzle velocity as the service
projectile). This is neglecting shot start, engraving, and friction
forces which are considerable, but which are relatively easy to
compensate for.
The invention can also be applied to recoiling barrel weapons by
anchoring the subcaliber barrel to the weapon frame rather than to
the weapon barrel.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a plan view in section of a cartridge case adaptor and a
subcaliber cartridge.
FIG. 2 is a plan view in section of the essential components of the
weapon.
FIG. 3 is a plan view in section of the subcaliber cartridge case
adaptor with a subcaliber cartridge loaded into the weapon.
FIG. 4 is a plan view in section of a first embodiment during
firing.
FIG. 5 is a plan view in section of a second embodiment during
firing.
FIG. 6 is a plan view in section of a third embodiment during
firing.
FIG. 7 is a partial plan view in section of a fourth embodiment
showing how any of the other embodiments are converted into a blank
firing adaptor.
FIG. 8 is like FIG. 7, but where a bulleted cartridge has
accidentally fired.
DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
Referring to FIG. 1, the outer configuration of a cartridge case
adaptor 18 fits the weapon feed system (not shown) and chamber. The
cartridge case adaptor 18 is provided with a subcaliber cartridge
chamber 34 with an enlarged chamber neck 68. The enlarged chamber
neck 68 is significantly larger in diameter than the cartridge case
neck of the subcaliber cartridge case 10 of the subcaliber
cartridge 36. The subcaliber cartridge chamber 34 of cartridge case
adaptor 18 is axially located in the cartridge case adaptor 18 to
receive a subcaliber cartridge 36 consisting of a subcaliber
projectile 32, a subcaliber cartridge case 10, with propellant 42
and a primer 16. The cartridge case adaptor 18 is reusable.
Referring to FIG. 2 the flash suppressor of the weapon barrel 22
has been replaced with a muzzle cap 28. Attached to muzzle cap 28
is a subcaliber barrel 24 with its centering ring 26. The
subcaliber barrel 24 is attached to the muzzle cap 28, so that when
assembled, the weapon barrel 22, muzzle cap 28 and subcaliber
barrel 24 do not move relative to each other. The centering ring 26
centers the subcaliber barrel 24 on the axis of the weapon barrel
22.
Referring to FIG. 3 a cartridge case adaptor 18 with a subcaliber
cartridge 36 has been placed in the weapon barrel 22. Weapon bolt
20 is in contact with the base of cartridge case adaptor 18 and
with the base of the subcaliber cartridge 36. The front of
projectile 32 has entered the rear of the bore of subcaliber barrel
24. Since the weapon is not locked, but is blowback operated, the
mass of the weapon bolt 20 supports the cartridge case adaptor 18
with its subcaliber cartridge 36 in the weapon barrel 22.
Referring to FIG. 4 the first embodiment of the subcaliber device
of FIGS. 2 and 3 is in the act of firing. The burning propellant
has generated pressurized gas 52 applying sufficient force to
expand the unsupported neck of the cartridge case 10 against the
enlarged chamber neck 68, releasing pressurized gas 52 past the
base of subcaliber projectile 32 into the volume between a second
primary booster area 44 and a first primary booster area 54 of
subcaliber barrel 24. Pressurized gas 52 also acts against the base
38 of subcaliber projectile 32 to provide shot start, projectile
engraving and to drive the projectile through the bore of
subcaliber barrel 24. The pressurized gas 52, acting equally in all
directions also applies pressure against the projected area 46
equal to the area of the diameter of the inside of the neck of
subcaliber cartridge case 10 at the enlarged chamber neck 68. The
total force of the pressurized gas 52 acting through the cartridge
case adaptor 18 against the weapon bolt 20 is the sum of the force
applied to the projected area 46 plus the force applied to the
projected area 44 of the primary booster.
Referring to FIG. 5 as the second subcaliber device embodiment
which provides power to the weapon bolt 20 for a longer period of
time than the first embodiment for a given subcaliber cartridge.
The burning propellant has generated pressurized gas 52 applying
sufficient force against the base 38 of subcaliber projectile 32 to
provide shot start, projectile engraving and to drive the
projectile through the bore of subcaliber barrel 24. The
pressurized gas 52, acting equally in all directions also applies
pressure against the projected area 46 equal to the area of the
base 38 of the subcaliber projectile 32. The pressurized gas 52
also acts against the first primary booster area 54 of the
subcaliber barrel 24, and against the projected second primary
booster area 44 of the cartridge case adaptor 18. A subcaliber
chamber vent 12 is provided, connecting a subcaliber cartridge
chamber 34 with a secondary booster chamber 14. The wall of the
subcaliber cartridge case 10, at the subcaliber chamber vent 12, is
not strong enough to contain the full pressure of the pressurized
gas 52. The pressurized gas 52 causes the wall of the cartridge
case 10 to fail at the subcaliber chamber vent 12, releasing
pressurized gas into a secondary booster chamber 14 and
pressurizing booster chamber 14 to apply pressure against projected
area of secondary booster chamber 40. With the fast burning powder
used, (such as Hercules Unique, Hercules Bullseye or
Winchester-Western 296 ball powder) rupture of the subcaliber
cartridge case wall takes place virtually at the moment of shot
start of subcaliber projectile 32.
Making the subcaliber chamber vent 12 small results in temporarily
trapping high pressure gas within the secondary booster chamber 14
after the projectile 32 has exited the muzzle of the subcaliber
barrel 24. This corresponds to gas expansion type gas operated gun
mechanisms. In other applications, making the subcaliber chamber
vent 12 large causes the subcaliber cartridge case 10 to vent
quickly into the secondary booster chamber 14 after firing, and to
vent quickly back into the subcaliber cartridge chamber 34 upon
muzzle exit of subcaliber projectile 32, corresponding to gas
impingement type gas operated gun mechanisms. The total force of
pressurized gas 52 acting through cartridge case adaptor 18 against
weapon bolt 20 is the sum of the force applied to the projected
area of the subcaliber bore 46 plus the force applied to the
projected area 44 of the primary booster plus the force applied to
the projected area 40 of the secondary booster chamber 14.
A rebound spring 50 can be provided to assist in arresting the
weapon bolt 20 as weapon bolt 20 goes into battery, compressing the
rebound spring 50 and storing some of the energy of the
counter-recoiling weapon bolt 20. The potential energy stored in
rebound spring 50 is later given back to boost recoil of weapon
bolt 20 at the time of firing.
Referring to FIG. 6 as the third subcaliber device embodiment which
provides for venting excess gas if a standard rifle or machine gun
cartridge is used in the design. The burning propellant has
generated pressurized gas 52 applying sufficient force against the
base 38 of subcaliber projectile 32 to provide shot start,
projectile engraving and to drive subcaliber projectile 32 through
the bore of subcaliber barrel 24. The pressurized gas 52, acting
equally in all directions also applies pressure against the
projected area 46 of subcaliber projectile base 38. The pressurized
gas 52 also acts against primary booster area 54 of subcaliber
barrel 24, and against the projected primary booster area 44 of the
cartridge case adaptor 18. A subcaliber chamber vent 12 is provided
which connects the subcaliber cartridge chamber with the secondary
chamber 14 which is vents through a booster vent 48 and thence
through muzzle cap vent 30 in muzzle cap 28.
The total force of the pressurized gas 52 acting through the base
of subcaliber cartridge case 10 and cartridge case adaptor 18
against weapon bolt 20 is the sum of the force applied to the
projected area of the subcaliber bore 46 plus the force applied to
the projected area 44 of the primary booster. There is negligible
force applied to the projected area 40 of the secondary booster
chamber 14 because the pressurized gas 52 is released from
secondary booster chamber 14 through secondary booster vent 48,
centering ring vent 58 and muzzle cap vent 30.
Referring to FIG. 7 which shows the subcaliber device adapted to
serve as a blank firing adaptor. A vented restrictor disc 60 has
been placed into the front of muzzle cap 28. The restrictor disc 60
is retained by a vented muzzle plug 66 which is secured to muzzle
cap 28. Vented restrictor disc 60 is provided with a vent hole 62.
Upon firing of a blank cartridge in the chamber, not shown,
pressurized gas will fill the bore of subcaliber barrel 24. The
pressurized gas will apply sufficient force to the cartridge case
adaptor, not shown, to power the weapon. The vent hole 62 of vented
restrictor disc 60 is sized to retain enough pressurized gas to
operate the weapon and to release the remaining gas to make noise
to simulate muzzle blast.
The vented muzzle plug 66 is provided with a bullet trap 64
sufficient to arrest the projectile if a bulleted cartridge is
accidentally fired.
Referring to FIG. 8 which is like FIG. 7, but where a bulleted
cartridge has accidentally been fired. The projectile 32 has
perforated vented rupture disc 60. Projectile 32 has been arrested
in bullet trap 64 of vented muzzle plug 66. The pressurized gas 52
is passing through the large hole created in the vented restrictor
disc 60 by projectile 32. The pressurized gas 52 is vented to the
atmosphere through muzzle plug vents 70 in vented muzzle plug
66.
NOMENCLATURE LIST
10 Subcaliber cartridge case
12 Subcaliber chamber vent
14 Secondary booster chamber
16 primer
18 cartridge case adaptor
20 weapon bolt
22 weapon barrel
24 subcaliber barrel
26 centering ring
28 muzzle cap
30 muzzle cap vent
32 subcaliber projectile
34 subcaliber cartridge chamber
36 subcaliber cartridge
38 base of subcaliber projectile
40 projected area of secondary booster chamber
42 propellant
44 primary booster
46 projected area of subcaliber bore
48 secondary booster vent
50 rebound spring
52 pressurized gas
54 primary booster area of subcaliber barrel
56 secondary booster area of subcaliber barrel
58 centering ring vent
60 vented restrictor disc
62 hole in vented restrictor disc
64 bullet trap
66 vented muzzle plug
68 enlarged subcaliber chamber neck
70 muzzle plug vent
* * * * *